The 60 GHz band is an unlicensed band that features a large amount of bandwidth, which means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications that require transmission of a large amount of data can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking station, wireless Gigabit Ethernet, and many others. The objective of the industry is to integrate 60 GHz band applications with portable devices including, but not limited to, netbook computers, tablet computers, smart-phones, laptop computers, and the like. The physical size of such devices is relatively small, and thus the area for installing additional circuitry to support 60 GHz applications is limited; therefore circuits that should be fabricated on a radio frequency IC (RFIC) should be carefully selected.
One of the elements typically included in a RFIC designed for millimeter-wave frequencies is a power and/or voltage detector. As illustrated in FIG. 1, a detector 100 is typically coupled between a power amplifier 110 and an antenna 120 using a probe 130. The detector 100 and probe 130 are on-chip, which means that they are part of the RFIC. On-chip power detection circuits are implemented at millimeter-wave frequencies on the RFIC mainly for performing automatic gain control that mitigates the impact of fabrication process, voltage, and temperature variations, enabling a built-in self-test (BIST) for low-cost and high-volume production, and for voltage standing wave ratio (VSWR) protection.
Existing solutions for on-chip power detection use a coupler-based probe 130. This type of probe includes capacitors that are integrated inside the amplifier's 110 output transmission lines 101. The probe 130 senses the voltage at the output of the amplifier 110, and then the voltage is converted into power measured by the detector 100. The measured power is proportional to the power of the RF signal at the output of the power amplifier 110.
The signal power detection requires squaring and filtering to measure the signal's root mean square (RMS) value. The detector 100 is indirectly connected to the sensed signal (i.e., through the probe 130), thus it introduces additional load between the amplifier 110 and the antenna 120. In millimeter wave RFICs, any additional load to a RF circuit has a significant impact on return and insertion losses, thereby reducing the circuit's performance. Therefore, the detector 100 should be carefully designed so that its operation would not adversely impact the other electrical components in the circuit under test. Specifically, the detector squares the sensed signal, an operation that results with a signal that includes various components to its outputs. For example, the frequency components may include direct current (DC), the signal main frequency (e.g., 60 GHz) and its harmonies. All frequencies except the DC must be filtered to avoid any aberrational RF signals to be transferred from the output of the detector, as such signals may induce, for example, noise and distortions in the circuit. Furthermore, the detector's load is not always modeled to RF frequencies, so its behavior cannot be properly predicated in simulations unless aberrational RF signals are eliminated.
Examples for power detection techniques using a coupler-based probe can be found in “A 60 GHz 65 nm CMOS RMS Power Detector for Antenna Impedance Mismatch Detection” to Gorisse, et al. and “A 20 dBm Fully-Integrated 60 GHz SiGe Power Amplifier With Automatic Level Control” to Pfeiffer, et al.
One of the drawbacks of the conventional RMS detectors, such as those described in the above-referenced documents, is that the proposed detectors use P-type metal-oxide-semiconductor (PMOS) components within the millimeter-wave section of the circuit. However, such devices require very good RF models in the main frequency of the signal being measured. A model (or a high frequency model) for any PMOS component is necessary in order to guarantee a good match between a simulated circuit and a silicon-fabricated circuit. Such a model usually includes a core model, provided by the factory, and a RF model for additional RF components. The RF models, specifically for PMOS and NMOS devices in the 60 GHz frequency band, are not provided by the factory, thus should be determined by the IC designer. However, the process of RF modeling for PMOS devices requires several tape-outs, directed measurements, proper de-embedding techniques, fitting processes, and so on. This a costly and time consuming task.
In addition, the on-chip power detection circuits discussed in the related art are based on coupler-based probes. The drawbacks of the coupler-based probes are that probing signals involve voltage coupling, hence the coupler (or probe) affects the sensed signals and the RF path between the amplifier and antenna. That is, the coupler degrades the RF signal and changes the impedance characteristics of the transmission line, thereby causing RF signal losses. In millimeter-wave RFICs, signal losses should be minimized to enable proper operation of the device. With this aim, a capacitive coupler probe should be carefully designed to mitigate the RF losses and changes to the characteristic impedance of the transmission line. However, this is a tedious task that cannot always resolve the above problems, due for example, to other constraints of the design.
Therefore, it would be advantageous to provide an efficient solution for voltage sensing and power detection of millimeter-wave signals that would overcome the drawbacks of conventional on-chip power detection circuits.